Lignin is the second most abundant natural polymer on earth. Industries using lignocellulosic biomass as feedstock generate a considerable amount of lignin as a byproduct with minimal usage. For a sustainable biorefinery, the lignin must be utilized in improved ways. Lignin is recalcitrant to degradation due to the complex and heterogeneous structure. The depolymerization of lignin and its conversion into specific product stream are the major challenges associated with lignin valorization. The blend of oligomeric, dimeric and monomeric lignin-derived compounds (LDCs) generated during depolymerization can be utilized by microbes for production of bioproducts. In the present study, a novel bacterium Burkholderia sp. strain ISTR5 (R5), a proteobacteria belonging to class betaproteobacteria, order Burkholderiales and family Burkholderiaceae, was isolated and characterized for the degradation of LDCs. R5 strain was cultured on 12 LDCs in mineral salt medium (MSM) supplemented with individual compounds such as syringic acid, p-coumaric acid, ferulic acid, vanillin, vanillic acid, guaiacol, 4-hydroxybenzoic acid, gallic acid, benzoic acid, syringaldehyde, veratryl alcohol and catechol. R5 was able to grow and utilize all the selected LDCs. The degradation of selected LDCs was monitored by bacterial growth, total organic carbon (TOC) removal and UV–Vis absorption spectra in scan mode. TOC reduction shown in the sample contains syringic acid 80.7%, ferulic acid 84.1%, p-coumaric acid 85.9% and benzoic acid 83.2%. In UV–Vis absorption spectral scan, most of the lignin-associated peaks were found at or near 280 nm wavelength in the obtained absorption spectra. Enzyme assay for the ligninolytic enzymes was also performed, and it was observed that lignin peroxidase and laccase were predominantly expressed. Furthermore, the GC–MS analysis of LDCs was performed to identify the degradation intermediates from these compounds. The genomic analysis showed the robustness of this strain and identified various candidate genes responsible for the degradation of aromatic or lignin derivatives, detoxification mechanism, oxidative stress response and fatty acid synthesis. The presence of peroxidases (13%), laccases (4%), monooxygenases (23%), dioxygenase (44%), NADPH: quinone oxidoreductases (16%) and many other related enzymes supported the degradation of LDCs. Numerous pathway intermediates were observed during experiment. Vanillin was found during growth on syringic acid, ferulic acid and p-coumaric acid. Some other intermediates like catechol, acetovanillone, syringaldehyde and 3,4-dihydroxybenzaldehyde from the recognized bacterial metabolic pathways existed during growth on the LDCs. The ortho- and meta cleavage pathway enzymes, such as the catechol-1,2-dioxygenase, protocatechuate 3,4-dioxygenase, catechol-2,3-dioxygenase and toluene-2,3-dioxygenase, were observed in the genome. In addition to the common aromatic degradation pathways, presence of the epoxyqueuosine reductase, 1,2-epoxyphenylacetyl-CoA isomerase in the genome advocates that this strain may follow the epoxy Coenzyme A thioester pathway for degradation.

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Burkholderia sp的基因组分析。ISTR5 用于木质素衍生化合物的生物漏斗

木质素是地球上第二丰富的天然聚合物。使用木质纤维素生物质作为原料的工业会产生大量木质素作为副产品，且用量最少。对于可持续的生物精炼厂，必须以改进的方式利用木质素。由于复杂且异质的结构，木质素难以降解。木质素的解聚及其转化为特定产品流是与木质素增值相关的主要挑战。解聚过程中产生的低聚、二聚和单体木质素衍生化合物 (LDC) 的混合物可被微生物用于生产生物产品。在本研究中，一种新型细菌 Burkholderia sp。菌株 ISTR5 (R5)，一种变形菌，属于β变形菌纲，伯克霍尔德菌目和伯克霍尔德菌科，被分离并表征为最不发达国家的降解。R5 菌株在矿物盐培养基 (MSM) 中的 12 个 LDC 上培养，添加了单独的化合物，例如丁香酸、对香豆酸、阿魏酸、香草醛、香草酸、愈创木酚、4-羟基苯甲酸、没食子酸、苯甲酸、丁香醛、藜芦醇和儿茶酚。R5 能够发展和利用所有选定的最不发达国家。通过扫描模式下的细菌生长、总有机碳 (TOC) 去除和 UV-Vis 吸收光谱监测选定 LDC 的降解。样品中显示的 TOC 减少量包含 80.7% 的丁香酸、84.1% 的阿魏酸、85.9% 的对香豆酸和 83.2% 的苯甲酸。在紫外-可见吸收光谱扫描中，在获得的吸收光谱中，大多数木质素相关峰出现在或接近 280 nm 波长处。还进行了木质素分解酶的酶测定，观察​​到主要表达木质素过氧化物酶和漆酶。此外，对 LDC 进行 GC-MS 分析以鉴定这些化合物的降解中间体。基因组分析显示了该菌株的稳健性，并确定了负责芳香或木质素衍生物降解、解毒机制、氧化应激反应和脂肪酸合成的各种候选基因。过氧化物酶 (13%)、漆酶 (4%)、单加氧酶 (23%)、双加氧酶 (44%)、NADPH：醌氧化还原酶 (16%) 和许多其他相关酶的存在支持 LDC 的降解。在实验过程中观察到许多途径中间体。在丁香酸、阿魏酸和对香豆酸的生长过程中发现了香草醛。其他一些中间体，如儿茶酚、乙酰香草酮、丁香醛和来自公认的细菌代谢途径的 3,4-二羟基苯甲醛，在 LDC 的生长过程中存在。在基因组中观察到邻-和间位切割途径酶，例如儿茶酚-1,2-双加氧酶、原儿茶酸3,4-双加氧酶、儿茶酚-2,3-双加氧酶和甲苯-2,3-双加氧酶。除了常见的芳香族降解途径外，基因组中存在环氧奎奥苷还原酶、1,2-环氧苯乙酰辅酶A异构酶表明该菌株可能遵循环氧辅酶A硫酯途径进行降解。在基因组中观察到儿茶酚-1,2-双加氧酶、原儿茶酸3,4-双加氧酶、儿茶酚-2,3-双加氧酶和甲苯-2,3-双加氧酶。除了常见的芳香族降解途径外，基因组中存在环氧奎奥苷还原酶、1,2-环氧苯乙酰辅酶A异构酶表明该菌株可能遵循环氧辅酶A硫酯途径进行降解。在基因组中观察到儿茶酚-1,2-双加氧酶、原儿茶酸3,4-双加氧酶、儿茶酚-2,3-双加氧酶和甲苯-2,3-双加氧酶。除了常见的芳香族降解途径外，基因组中存在环氧奎奥苷还原酶、1,2-环氧苯乙酰辅酶A异构酶表明该菌株可能遵循环氧辅酶A硫酯途径进行降解。